Ethylene oxide purification

ABSTRACT

An improved process for the recovery of high-purity ethylene-oxide water feed streams to EO purification and MEG reaction units when both are operating in EO plants that incorporate EO Stripper bypass technology, by installing a second lights stripper to exclusively degasify the diluted EO feed to the MEG reactor, thus permitting the use of additional bypassed (gasified) EO absorbate as the diluent and resulting in a substantial increase in the total amount of EO absorbate that can bypass the EO Stripper.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a U.S. Divisional Application of U.S. application Ser. No.17/760,680, filed Mar. 15, 2022, which is the U.S. National Phaseapplication of PCT/US2020/49136, filed 3 Sep. 2020, which claimspriority to U.S. Provisional Patent Application No. 62/900,952, filed 16Sep. 2019, entitled “ETHYLENE OXIDE PURIFICATION” the contents of eachof which are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

This invention relates to a method of improving the purity of theethylene oxide (EO) recovered from the gaseous effluent from an ethyleneoxide reactor of a combined ethylene oxide/ethylene glycol plant whenthe purified gaseous effluent is recovered as aqueous ethylene oxidesolutions and used as feeds to both ethylene oxide purification columnsand to ethylene glycol units that are integrated into the combinedethylene oxide/ethylene glycol plant. The method relates to improvingboth the ethylene oxide stripping system and the ethylene oxidereabsorption system to reduce operating costs and providesimplifications to the overall operation of the combined ethyleneoxide/ethylene glycol plant. Such ethylene oxide stripping and ethyleneoxide reabsorption systems are commonly used in the EO recovery step toproduce two pure ethylene oxide-water feed streams with differing EOconcentrations. One stream is used as feed to a column or series ofcolumns that further purify the EO to produce high purity EO and theother, lower concentration stream is used as the feed to an ethyleneglycol plant that produces polyester fiber grade ethylene glycol.

BACKGROUND OF THE INVENTION

When ethylene oxide (EO) is produced by silver-catalyzed, vapor-phasepartial oxidation of ethylene by molecular oxygen, the EO product is ina hot gaseous effluent stream from the reactor. The ethylene oxidecontent in this reactor effluent is quite low and therefore requiresrecovery, further purification and must be concentrated as well. Thisrecovery of the ethylene oxide from the reactor effluent gas, asconventionally practiced, involves cooling of the reaction effluentgases in a heat exchanger train and absorption in water. The waterabsorption step produces a very dilute EO solution together with variousimpurities. Ethylene oxide is then stripped from this dilute solutionand the EO gas thus stripped is then reabsorbed in recycled EO-freeprocess water to produce the more concentrated EO solutions required tobe fed to the columns producing the high purity EO and also to be fed tothe plant that produces fiber-grade ethylene glycol.

As described in U.S. Pat. No. 7,569,710, the entire contents of whichare incorporated by reference herein for all purposes, the cooled EOreactor effluent gas is sent to an EO absorber, which may contain aquench section in the lower part of the absorber column where thereactor effluent is scrubbed with a recirculated, cooled aqueousalkaline stream to absorb and neutralize acidic compounds such as aceticand formic acids and also to absorb almost all of the trace amount ofby-product formaldehyde (which is present as methylene glycol) prior tomoving through the upper section of the EO absorber column. Also asdisclosed in U.S. Pat. No. 7,569,710, the reactor effluent may be passedthrough a separate quench column where the same scrub with an alkalinestream is performed, before being passed to the absorber.

A liquid bleed stream is removed from the quench (also called a scrubberor a quench scrubber) step. This is done whether a separate alkalinequench column is used or if the alkaline quench scrubbing step isperformed in the bottom of the absorber column. The purpose of thisbleed is to remove the extra water that would otherwise accumulate inthe recirculation loop. This water is formed as a by-product during theoxidation of ethylene to ethylene oxide. This by-product water is almostall condensed during the quenching/scrubbing step.

Then, the treated vaporous reaction stream from the alkaline quenchscrub step is passed through liquid de-entrainment devices and fed to awater wash step where it is washed with fresh process water to removeany entrained quench liquid and to absorb any remaining formaldehydevapor. After this washing step, the vaporous reaction stream is passedthrough liquid de-entrainment devices and then fed to the bottom of anethylene oxide absorber column, where it is counter-currently washedwith recirculated, EO-free process water to absorb the ethylene oxideand produce a high-purity EO-containing absorbate. The quench bleed,which in addition to the water mentioned above, contains typically 0.5-5wt. % of EO and comparable concentrations of glycol and sodium salts aswell as a low concentration of formaldehyde (as methylene glycol) issent to a quench bleed stripper where the EO is stripped out andrecovered. The EO-free quench stripper bottoms can then be disposed ofas a waste stream or processed separately for recovery of the smallquantity of crude ethylene glycol that it contains.

In EO reaction systems that include an EO stripper bypass stream flowscheme (as described in U.S. Pat. No. 7,569,710), the EO absorbate (i.e.a water/ethylene oxide solution) from the EO absorber is pure enough tobe fed directly to the purification column(s) that produce high purityethylene oxide (HPEO) and/or reactors that produce ethylene glycol.However, while the purity of this aqueous solution is acceptable, theconcentration of EO in the water is normally too low for either of theseprocess routes to be economically feasible. Accordingly, in theseplants, only part of the dilute EO absorbate is sent directly to the EOreabsorber, bypassing the main EO stripper. The balance of the EOabsorbate is fed to the EO Stripper to produce concentrated EO vaporthat, when reabsorbed in the bypassed EO absorbate, will raise its EOconcentration to the higher levels required in the feed to an EOpurification system and/or a glycol reactor.

The concentrated EO bottoms from the EO reabsorber, which contain smallconcentrations of absorbed CO₂ and reaction gases, are then normally fedto a single lights stripper in which low pressure steam is injected tostrip out the CO₂ and other light components before being pumped to thehigh purity ethylene oxide (HPEO) purification column and/or the reactorthat produces ethylene glycol, also referred to as monoethylene glycol(MEG).

The most suitable EO concentration in the feed to a large, single highpurity ethylene oxide (HPEO) purification column, such as described inU.S. Pat. No. 4,134,797, the entire contents of which are incorporatedby reference herein for all purposes, is normally in the range of 10-13wt. % in water, whereas the normal EO concentration range in the feed toan MEG reactor would be in the range 6-10 wt. % EO in water. The higherwater to EO ratio is desirable in order to limit the production ofheavier glycols.

Accordingly, when both the column that produces high purity ethyleneoxide and the reactor that produces fiber grade monoethylene glycol areoperating at comparable ethylene oxide equivalent (EOE) capacities withsimilar net feed rates of ethylene oxide, but with the differentrequired EO concentrations in their feed streams, the EO reabsorberwould normally be operated to produce EO reabsorber bottoms feed to thesingle lights stripper with the higher EO concentration required by theHPEO Column. This is the controlling EO concentration that thereforesets and limits the amount of EO absorbate that can bypass the EOstripper in a plant that uses this process scheme. The desired moredilute EO feed to the MEG reactor is then produced by mixing part of thebottoms from the lights stripper with EO-free recycle process water.

However, even with the benefits of utilizing the EO process thatincorporates the EO bypass flow scheme, there is still scope for processimprovements in terms of energy efficiency and simplification of theprocess.

SUMMARY OF THE INVENTION

The present invention provides an improved method of purification ofethylene oxide which comprises quenching and washing the ethylene oxidereactor effluent by contact with a recirculated, cooled, aqueousalkaline stream and a water wash, passing the gaseous ethylene oxidecontaining stream obtained from the alkaline quenching wash to anethylene oxide absorber. In the ethylene oxide absorber, the ethyleneoxide is absorbed in once-through EO-free process water to form a diluteaqueous ethylene oxide-containing absorbate solution. Next, a portion ofthis ethylene oxide-containing dilute absorbate solution is stripped inan EO stripper to produce a gaseous ethylene oxide overhead vapor. Thegaseous ethylene oxide overhead vapor is then passed to an ethyleneoxide reabsorber where the ethylene oxide is absorbed in another portionof the dilute aqueous ethylene oxide-containing absorbate which bypassedthe EO stripper. Thus, an EO aqueous reabsorbate solution having ahigher content of EO than the ethylene oxide-containing dilute absorbatesolution emerges from the EO reabsorber. A portion of thisenriched-in-EO reabsorbate solution passes to a first lights stripperdesigned to remove dissolved carbon dioxide with a lights-free,concentrated ethylene oxide-containing solution being recovered for useas high-purity feed to only a high purity EO distillation system.

In a preferred embodiment, from 10-90%, more preferably 20-80%, and mosttypically 25-35% of the dilute ethylene oxide solution obtained from theabsorber is passed directly to the reabsorber, and never passes throughthe EO stripper, thus reducing the stripping steam consumed in the EOStripper by 25-35%.

Additionally, another portion of the reabsorber bottoms (i.e. the EOenriched absorbate) is mixed with additional bypassed dilute EOabsorbate (that bypasses both the EO stripper and the EO reabsorber) andan acetaldehyde-EO purge from the high purity EO distillation system.This gasified mixture is fed to a second lights stripper that will thenproduce lights-free aqueous bottoms containing a lower EO concentrationthan the feed to the high purity EO distillation system. This lower EOconcentration is the correct, lower concentration of EO/higherconcentration of water that the MEG reactor requires to reduce the yieldof heavier glycols. This entire process which also serves to dilute theEO stream fed to the glycol reactor also substantially increases thetotal quantity of dilute EO absorbate that bypasses the EO stripper andtherefore reduces the stripping steam that is required by the EOstripper.

In another preferred embodiment, an additional 5-60%, more preferably7-40%, and most typically 10-25% of the dilute ethylene oxide solutionobtained from the EO absorber bypasses both the EO stripper and the EOreabsorber and is mixed with surplus EO reabsorber bottoms and theacetaldehyde-EO purge stream from the HPEO Column and passed directly toa second lights stripper for use as feed to the glycol reactor, andnever passes through the EO stripper or the EO reabsorber, thus reducingthe stripping steam consumed in the EO stripper by an additional 10-25%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows how the maximum potential EO stripper bypass rates (and therelated stripper steam savings) are related to the EO concentration inthe EO reabsorber bottoms;

FIG. 2 is a schematic representation of a flow scheme for an EO reactionsystem that includes an EO Stripper Bypass stream and a single LightsStripper that produces the EO feeds for both the EO Purification Columnand the MEG reactor;

FIG. 3 is a schematic representation of an exemplary embodiment of theinvention showing a flow scheme which is the process as shown in FIG. 2with the addition of a second Lights Stripper; and

FIG. 4 is a graph showing the effect of increasing the water:EO ratio onthe glycol reactor product distribution.

DETAILED DESCRIPTION

According to embodiments of the invention, incorporation of anadditional lights stripper into a combined ethylene oxide/ethyleneglycol plant that utilizes a stream that bypasses the ethylene oxidestripper column permits a greater percentage of the ethylene oxide tonot only bypass the ethylene oxide stripper column, but also to bypassthe ethylene oxide reabsorber column. FIG. 1 shows how the maximumpotential EO Stripper Bypass rates (and the related stripper steamsavings) are related to the EO concentration in the EO Reabsorberbottoms. This plot demonstrates the energy savings that may be realizedby the production scheme in FIG. 3 as compared to the scheme in FIG. 2 .This is because a portion of the EO absorbate from the initial EOabsorber column 1300 can bypass both the EO stripper 1311 and the EOreabsorber 1327 in the FIG. 3 scheme. In the FIG. 2 scheme, a portion ofthe EO absorbate from the initial EO absorber column 300 can bypass onlythe EO stripper 311. Therefore in the inventive scheme, shown in FIG. 3, the total amount of EO absorbate that can be bypassed is 40-60 weight% of the process stream compared to 20-30% weight percent in the FIG. 2scheme.

An exemplary ethylene oxide recovery process as described in U.S. Pat.No. 7,569,710 that has an ethylene oxide bypass stream is shown in FIG.2 . This process will be described in detail, since the inventiveprocess comprises certain elements of this process.

Generally, the process as shown in FIG. 2 depicts a process of purifyingand concentrating the effluent from a catalytic reactor that oxidizesethylene gas to ethylene oxide, but includes an ethylene oxide bypassstream, i.e. a stream that bypasses the main EO stripping column. As isknown in the art, impurities in the reaction effluent that arebyproducts of the oxidation reaction and other side reactions mayinclude water, carbon dioxide, various aldehydes, e.g. formaldehyde andacetaldehyde, as well as organic acids, among others. These need to beremoved and in addition, the purified ethylene oxide needs to beprovided in the correct concentrations in order to be suitable forfurther purification steps, and/or to be fed to a reactor that produceshigh grade ethylene glycol, or mono ethylene glycol (also referred to asEG or MEG) that is suitable to be used in the production of fiber-gradepolyester. Utilizing the process described below allows some of theethylene oxide stream from an ethylene oxide absorber to bypass anethylene oxide stripper column, be diluted with clean process water andgo directly to a glycol reactor.

Referring to FIG. 2 , effluent gas containing ethylene oxide from an EOreaction system (not shown) is introduced directly into the bottomsection of a quench scrub section 352 of a column 300 via conduit 302.Note that in this embodiment, the quench (or quench scrub) section 352comprises the bottom of the column 300, but in alternative embodiments,the quench scrubbing step could be performed in a separate dedicatedcolumn. Quench bottoms solution is recirculated via conduits 353 and355A, through cooler 354, and conduits 355B and 357 to the top of thequench scrubbing section 352 of the column 300. This is clear in FIG. 2where conduit 357 is shown entering the absorber column 300 at a pointabove the bottom, but well below the top of column 300.

An alkaline solution, in the form of concentrated sodium hydroxide (forinstance, 10-20 wt. % as an aqueous solution) is injected into therecirculated quench solution via conduit 356. The NaOH neutralizesdissolved CO₂ which is present as a contaminant and thus converts intosodium carbonate and sodium bicarbonate. The basic solution alsoneutralizes organic acids, which are likewise are present ascontaminants from the oxidation reaction. A cooled, scrubbed vapor,which is free of organic acid vapor, but contains some formaldehyde andentrained quench liquid, thus emerges from the top of the quench section352 and is passed through a demister unit 359 to remove the entrainedliquid. This cooled, scrubbed vapor then enters an upper water washsection 361 above the quench section 352 of the column 300.

The filtered quench gas is then washed in water wash section 361 withfresh purified water, that is introduced via conduit 362. This waterremoves any remaining entrained quench liquid and absorbs most of theremaining formaldehyde and water-soluble heavy impurities. Acountercurrent water wash will preferably be used for this step. Thiscountercurrent water wash step may optionally be preceded by arecirculated water wash section for maximum vapor-liquid contact. Thenet wash water from the bottom of the water wash section(s) may draininto the top of the lower quench section 352. This water thus dilutesthe concentration of formaldehyde and other undesirable impurities inthe quench liquid and accordingly reduces the equilibrium concentrationof these impurities in the scrubbed gas feed to the EO absorber section303 located in the upper section of column 300. The net quench bottomssolution bleed stream, containing condensed water, wash water, absorbedimpurities and some ethylene oxide, flows via conduits 353 and 365 to aquench bleed stripper 366.

The quenched/scrubbed washed gas from the top of the water wash section,is passed through a second demister unit 363 to remove any entrainedwash water from conduit 362. This gas enters the EO absorber section303. Cold EO-free absorption water is introduced into the upper sectionof absorber section 303 via conduit 321B. The quenched/scrubbed washedgas (i.e. reaction effluent gas after passing through sections 352 and361 of column 300) is counter-currently contacted by the cold absorbentwater to absorb almost all of the ethylene oxide entering the absorbersection 303 of column 300. The non-condensable, non-absorbable-in-watergas remaining from the reaction effluent gas leaving the top of absorber303 is essentially free of ethylene oxide and is returned to the EOreaction system via conduit 304. The dilute EO-water solution (i.e. theEO as absorbate) that is formed in absorber 303 is withdrawn from thebottom of the absorption section via conduit 305.

In the flow scheme shown in FIG. 2 , part of the EO absorbate in conduit305 bypasses EO stripper 311 and flows directly to an EO reabsorberbottoms recycle cooler 329 via conduits 310 and 333A. The amountbypassed will vary between 25-35 weight % of the total absorbatesolution exiting at conduit 305. The amount of absorbate solution thatbypasses the EO stripper 311 depends on the EO concentration in theabsorbate solution and depends on the desired EO concentration in thereabsorber bottoms (and feed to an EO purification unit or a glycolreactor). The amount bypassed can be determined using tables, equations,or graphs.

The balance of the absorbate solution (i.e., the portion that was notbypassed and sent to the cooler 329) is introduced into an EO stripperpreheater exchanger 307 via conduit 308, and the hot rich absorbatesolution, from preheater exchanger 307 is fed to an upper portion of EOstripper 311, via conduit 309. Stripping steam, which may be extractedfrom a downstream glycol plant, is introduced to a lower portion ofstripper 311 via conduit 338B or the stripping steam may be generatedinternally by a reboiler (not shown). By countercurrent contact of theabsorbate solution and steam within stripper 311, the absorbate solutionis stripped of the ethylene oxide, which together with steam, carbondioxide, light ends, and trace impurities is withdrawn from the top ofstripper 311 via conduit 313A. The stripped (lean) absorbate solution,now comprising water essentially free of ethylene oxide, is withdrawnfrom the bottom of stripper 311 via conduit 319A and cooled in heatexchanger 307, giving up heat to the rich absorbate solution feed. Thecooled lean absorbate solution from cooler 307 is passed via conduit319B, combined with recycled water from the glycol plant and/or the EOpurification tower 345 in conduit 321A to heat exchanger 320, where itis further cooled and the total lean (in EO) absorbate solution streamis recycled back to the top of absorber section 303 in column 300 viaconduit 321B.

The rich absorbate solution fed to the EO stripper 311 in conduit 309may contain from about 1 to about 5 wt. % of ethylene oxide and thestripper 311 is operated to recover more than 95% and usually more than99% of the ethylene oxide contained in the rich absorbate solution fedto the stripper 311. Although the stripper 311 normally operates atclose to atmospheric pressure, the temperatures in the stripper column311 are high enough to cause about 0.5-3.0% of the total amount of EO inthe solution of feed to thermally hydrate (i.e. react with the water) toform mainly monoethylene glycol. The glycol produced in the EO stripperwill build up to a low, equilibrium concentration in the EO absorber andEO stripper recycle water system that is controlled by the amount of theabsorbate solution that bypasses (via stream 310) the stripper, sincethis bypass stream effectively acts as a very large cycle water glycolbleed.

The overhead vapor withdrawn via conduit 313A from the EO stripper 311,usually contains about 20 to 30 mole % of ethylene oxide. The primarydiluent in this vapor stream is water, although about 7-10 mole % isgenerally non-condensable gases. These non-condensable gasespredominantly comprise CO₂, but also may include nitrogen, argon,oxygen, methane, ethylene and ethane. The overhead vapor stream inconduit 313A from stripper 311 is cooled in heat exchanger 312. The heatexchanger 312 will condense some of the water in the overhead vaporemerging from the stripper 311 and then a total effluent mixture of theuncondensed EO-rich portion of the vapor and the condensate flows fromthe heat exchanger 312 via conduits 313B and 316 to an EO reabsorber327.

The net quench bleed bottoms stream in conduit 353 from the quenchscrubber portion 352 of column 300 comprises mainly excess waterproduced as a byproduct of the EO reaction that is partially condensedin the quench scrubber portion 352 plus makeup wash water. The quenchbleed bottoms also comprises alkaline salts and absorbed ethylene oxide.This stream is sent, via conduit 365, to the small purge stripper 366where the absorbed ethylene oxide is stripped out, using stripping steamthat is injected into purge stripper 366 via conduit 371. The strippingsteam for purge stripper 366 may alternatively be generated in areboiler (not shown). A heat exchanger may be also used to preheat thestream fed to the purge stripper 366 in order to reduce the reboilerheat duty and/or to reduce the amount of stripping steam needed.

The overhead vapors emerging from the top of purge stripper 366 viaconduit 367 are cooled in heat exchanger (or condenser) 368 to atemperature that is low enough such that a substantial part, preferablyat least 60%, of the water contained in the overhead vapor from thepurge stripper 366 is condensed. This condensate phase from heatexchanger/condenser 368 is contaminated with dissolved salts andformaldehyde and is drained or pumped back into the upper portion of thepurge stripper 366 via conduit 369.

The remaining uncondensed portion of the cooled purge stripper overheadvapor is withdrawn from the heat exchanger/condenser 368 via conduit370. As can be seen in FIG. 2 , this uncondensed portion of the cooledpurge stripper overhead vapor in conduit 370 is then combined with theEO and condensate mixture that emerges via conduit 313B from the heatexchanger 312 on the overhead from the main EO stripper 311. The streamin conduit 381, which is an overhead vapor stream emerging from a lightsstripper 380, is also combined (via conduit 381A) with the streams inconduits 370 and 313B and a formaldehyde-rich stream in conduit 347(also via conduit 381A) that emerges from the top of an EO purificationunit 345. These four combined streams (conduits 370, 313B, 381 and 347)are introduced, via conduit 316, into a lower portion of the reabsorber327. The EO-free aqueous bottoms from purge stripper 366, which containsmost of the formaldehyde, salts, and a small amount of ethylene glycolare sent to waste treatment or technical grade glycol recovery viaconduit 372.

Some recycled cold water is introduced to an upper portion of thereabsorber 327 via conduit 351B. Within the upper portion of thereabsorber 327, the combined light gases in conduit 316 from theoverhead vapor streams from the EO stripper 311, the quench purgestripper 366, the lights stripper 380 and the EO purification column 345and the cold water from conduit 351B are counter-currently contacted toabsorb the maximum amount possible of the ethylene oxide contained inthe combined vapor streams of conduit 316. The non-condensed gasesemerging from the top of reabsorber 327, that normally contain onlytrace amounts of ethylene oxide are vented via conduit 328. Since thisvent stream in conduit 328 contains a significant amount ofhydrocarbons, comprising mainly ethylene and methane, it is preferablycompressed and recycled back to the EO reactor gas system for (partial)recovery of the contained ethylene. In some plants, particularly thosethat have a small production capacity, the reabsorber vent gas inconduit 328 may be vented to the atmosphere, or preferably incineratedto avoid atmospheric pollution.

The EO-rich reabsorbate is withdrawn from the bottom of reabsorber 327via conduit 330. This reabsorbate is pressurized using a pump (notdepicted) and divided into two portions shown as conduits 331 and 332. Aportion that is the net bottoms product (i.e., second portion of thebottoms are cooled and recycled back to the EO reabsorber 327) flowsthrough conduit 331 to the top of the lights stripper 380. The aqueousreabsorbate bottoms comprises not only the reabsorbed ethylene oxidevapor but also comprises acetaldehyde and dissolved carbon dioxide aswell as dissolved non-condensable gases. The mass balance of water inthe absorber-stripper system may be maintained by injecting low pressureprocess steam extracted from the glycol plant directly into the EOstripper 311 to provide up to 100% of the stripping vapor requiredand/or by recycling water from the glycol plant evaporation section foruse as absorption water.

As described in U.S. Pat. No. 4,134,797, the portion of the EO-richreabsorbate withdrawn via conduit 330 that goes into conduit 331 willfirst pass into the lights stripper column 380 (also referred to as thecarbon dioxide stripping column). In the lights stripper column 380 theliquid in conduit 331 is stripped of CO₂ and light gases, such as ethaneand ethylene. Stripping steam is supplied to the bottom of the lightsstripper column 380 from an evaporation train 337 via conduits 338 and338A. The CO₂-rich EO vapor that exits lights stripper 380 via conduit381 is combined with the overhead vapor purge from the EO purificationcolumn 345 in conduit 381A, is mixed with the main EO feed vapor streamin conduit 316 and then enters the bottom of reabsorber 327, asdescribed above. The essentially gas-free bottoms, (purified aqueoussolution of EO) from the carbon dioxide (lights) stripping column 380are then pumped to a glycol reaction unit 335 via conduits 382, 383, and334 and to the EO purification unit via conduits 382, 344A and 3448.Note however, that in this process, this bottoms stream in conduit 383is too concentrated in EO for the ethylene glycol reactor 335 and thattherefore it is diluted with process recycle water provided via conduit339A that originates from the evaporation train 337 to provide the finalfeed in conduit 334 to the glycol reactor 335.

In the reabsorber unit 327, the recycled reabsorbate flowing throughconduit 332 is combined with bypassed rich absorbate in conduit 333A,cooled in heat exchanger 329 and introduced as cold liquid to a middleportion of reabsorber 327 via conduit 3338. Heat exchanger 329 maintainsthe reabsorber in heat balance to achieve the pre-determined bottomreabsorbate temperature and hence the desired concentration of ethyleneoxide. Depending on the operating pressure of the reabsorber 327 and theamount of bypassed dilute absorbate in conduit 310, the ratio ofreabsorbate recycled via conduit 332 to the net reabsorbate withdrawnvia conduit 331 will range from as low as no recycle to as high as aratio of 3:1. The maximum bypass of EO-rich absorbate (not shown) may beachieved when the bypassed absorbate in stream 310 is separately cooledand introduced into reabsorber 327 at a point above the recycled bottomreabsorbate.

The reabsorbate in conduit 344A (from the bottoms of stripper 380 viaconduit 382) flowing to EO purification is preheated in heat exchanger343 and fed to the lower part of the single EO purification column 345via conduit 3448, where it is separated into a purified side-stream EOliquid product (stream 346), and a small formaldehyde-rich crude EOoverhead vapor purge stream (stream 347) that is recycled back to thereabsorber 327 for recovery of the EO, as described above. In addition,an impure side stream of acetaldehyde-rich EO is removed from the EOpurification column 345 via conduit 341 to purge the acetaldehyde.Although not shown, this stream is mixed with the stream in conduit 334and sent to the glycol reaction unit 335. The EO-free bottoms waterstream containing most of the trace amount of formaldehyde that was inthe feed to the EO purification column 345, is withdrawn via conduit349A, cooled in heat exchanger 343 and a portion is recycled to thereabsorber 327 via conduits 3498, 351A, and 3518. The EO free bottomsnot required in the reabsorber 327 are recycled via conduit 342 andcombined with recycle condensate from the evaporation train 337 inconduit 3398.

In the glycol reactor 335, the ethylene oxide in the degasified lightsstripper bottoms feed that has been mixed with recycle evaporatorcondensate via conduit 339A to increase the water-to-EO ratio (asrequired to reduce the formation of heavy glycols) and the smallacetaldehyde-EO purge in conduit 341 from the EO purification unit 345is almost completely reacted with water to form mixed ethylene glycols.The effluent from the glycol reactor 335 is fed to the multiple-effectevaporation train 337 in which the water is separated from theconcentrated crude glycol that is then fed to glycol purification (notshown) via conduit 340. Part of the water separated in evaporation train337 is recycled back to the EO plant as steam via conduit 338 andinjected directly into the lights stripper 380 (via conduit 338A) and EOstripper 311 (via conduit 338B) to provide up to 100% of the requiredstripping steam. The balance of the recovered evaporation water isrecycled back to the EO plant via conduit 339 and is combined with thebalance of the bottoms from EO purification column 345 in conduit 339B.To provide the required flow of absorption water to the EO absorber 303,makeup recycle water is added via conduits 339B, 339C, 321A and 321B andsurplus recycle water is sent to a recycle surge tank (not shown) viaconduit 339D.

An embodiment of the present invention as applied to plants that produceboth EO and mono-ethylene glycol as described above is shown in FIG. 3 .

Referring to FIG. 3 , effluent gas from the EO reaction system (notshown) containing ethylene oxide (EO) is introduced directly into abottom of quench/scrubbing section 1352 of column 1300 via conduit 1302.Quench bottoms solution is recirculated via conduits 1353 and 1355A,cooler 1354, and conduits 1355B and 1357 to the top of the quenchscrubbing section 1352. Concentrated sodium hydroxide (10-20 wt. %aqueous solution) is injected into the recirculated quench solution viaconduit 1356 to react with dissolved CO₂ and be converted into sodiumcarbonate and bicarbonate, which then neutralize byproduct organicacids. The cooled, scrubbed vapor from the top of the quench section1352, which is free of organic acid vapor, but contains someformaldehyde and entrained quench liquid is passed through a demisterunit 1359 to remove the entrained liquid and then enters the upper washsection 1361 above the quench section 1352 of the column 1300.

The filtered quench gas is then washed with fresh purified water,introduced via conduit 1362, to completely remove any remainingentrained quench liquid and to absorb most of the remaining formaldehydeand heavy impurities. A countercurrent water wash will preferably beused, which can be preceded by a recirculated water wash section formaximum vapor-liquid contact. The net wash water from the bottom of thewater wash section(s) in column 1300 may drain into the top of the lowerquench section 1352, diluting the concentration of formaldehyde andother undesirable impurities in the quench liquid and reducing theequilibrium concentration of these impurities in the scrubbed gas feedto the upper part of column 1300. The upper part of column is an EOabsorber section 1303. The net quench bottoms solution bleed, containingcondensed water, wash water, absorbed impurities and some ethyleneoxide, flows via conduits 1353 and 1365 to a quench bleed stripper 1366.

The washed vapor from the water wash section 1361, is passed through ademister unit 1363 in column 1300 to remove any entrained wash water andenters the EO absorber section 1303 of column 1300. Cold EO-freeabsorption water is introduced into the upper section of absorbersection 1303 via conduit 1321B and the reaction effluent gas is countercurrently contacted by the water to absorb almost all of the ethyleneoxide entering the absorber. Note that this water in conduit 1321B maybe recycled from an evaporation train 1337 which follows a glycolreactor 1335. The non-condensable reaction gas, comprising inter alia,unreacted ethylene, leaving the top of absorber section 1303 isessentially free of ethylene oxide and is returned to the EO reactionsystem via conduit 1304. The dilute EO-water solution (i.e. the EOabsorbate) that is formed in absorber section 1303 is withdrawn from thebottom of the absorption section 1303 via conduit 1305.

Optionally, the three sections of column 1300 may be comprised of two orthree separate columns.

Part of the EO absorbate in conduit 1305 bypasses EO stripper 1311 andflows directly to the EO reabsorber bottoms recycle cooler 1329 viaconduits 1310, 1326 and 1333A. The amount of EO absorbate in conduit1305 that bypasses the EO stripper 1311 may vary between 15-75%. Theamount of EO absorbate in conduit 1305 that can bypass the EO stripper1311 depends on the EO concentration in the EO absorbate and the desiredEO concentration in the reabsorber 1327 bottoms in conduit 1330 (andglycol reactor feed), and can be determined using tables, equations, orgraphs.

In this inventive flow scheme, a significant additional part of the EOabsorbate that exits the bottom of column 1300 will bypass both the EOstripper 1311 and the EO reabsorber 1327 and a first lights stripper1380 via conduit 1386 and go directly to a second lights stripper 1390.As can be seen in FIG. 3 , this EO absorbate that has bypassed the EOstripper 1311, the EO reabsorber 1327 and a first lights stripper 1380via conduit 1386 is used instead of recycled process water to dilute aportion of the more concentrated bottoms from EO reabsorber 1327provided by conduit 1387 in conduit 1388. By controlling the flow ofbypassed absorbate in conduit 1386, the diluted EO absorbate thatultimately emerges as the bottoms from the second lights stripper 1390has the desired lower EO concentration that may be fed directly to theglycol reactor 1335. The addition of the second lights stripper 1390 todegasify only the feed to the MEG reactor 1335 is therefore asignificant process improvement from the flow scheme as shown in FIG. 2and significantly increases the amount of EO absorbate that can bypassthe EO stripper 1311. This additional amount of process stream thatbypasses the EO stripper 1311 means that less heat and electrical energyis needed to operate the EO stripper 1311 and the EO reabsorber 1327compared to a process that does not utilize the second lights stripper1390 (also referred to as the MEG lights stripper). Notably, the totalenergy load on both strippers 1380 and 1390 is approximately the same asthe total of the single stripper 380 in FIG. 2 .

The balance of the EO absorbate that exits the column 1300, i.e., theportion of the EO absorbate stream from conduit 1305 that does NOTbypass the EO stripper 1311 and the EO reabsorber 1327, is introducedinto an EO stripper preheater exchanger 1307 via conduit 1308, and thehot EO absorbate from preheater 1307 is fed to an upper portion of theEO stripper 1311, via conduit 1309. Low pressure stripping steamextracted from a downstream glycol plant 1335 is introduced to a lowerportion of EO stripper 1311 via conduit 1338B. The stripping steam mayoptionally be generated internally by a reboiler (not shown). The waterbalance in the absorber-stripper system may be maintained by directlyinjecting low pressure process steam extracted from the glycol plant1335 directly into the EO stripper 1311 to provide up to 100% of thestripping vapor required and/or by recycling water from the glycol plantevaporation section 1337 for use as absorption water.

By countercurrent contact of the EO absorbate and steam within the EOstripper 1311, the EO absorbate is stripped of the ethylene oxide, whichtogether with steam, carbon dioxide, light ends and trace impurities iswithdrawn from the top of the EO stripper 1311 via conduit 1313A. Thestripped absorbate, now essentially free of ethylene oxide and thuscomprising mostly water with a small concentration of ethylene glycol,is withdrawn from the bottom of the EO stripper 1311 via conduit 1319Aand cooled in heat exchanger 1307, giving up heat to the rich absorbatefeed. The cooled lean aqueous absorbate from the heat exchanger 1307 ispassed via conduit 1319B, combined with recycled water from theevaporation train 1337 of the glycol plant and the EO purification tower1345 via conduit 1339C, and finally, in conduit 1321A is passed to heatexchanger 1320, where it is further cooled and the total lean aqueousabsorbate stream is recycled back to top of absorber section 1303 viaconduit 1321B.

The rich (in EO) absorbate feed in conduit 1309 to the EO stripper 1311may contain from about 1 to about 5 wt. % of ethylene oxide and the EOstripper 1311 is operated to recover more than 95% and usually more than99% of the ethylene oxide contained in the feed. Although the EOstripper 1311 normally operates at close to atmospheric pressure, thetemperatures in the EO stripper column 1311 are high enough to thermallyhydrate in the range of 0.5-3.0% of the EO feed to ethylene glycol. Theglycol thus produced in the EO stripper 1311 will build up to a low,equilibrium concentration in the EO absorber-EO stripper recycle watersystem that is controlled by the amount of the absorbate that bypassesthe EO stripper 1311 via stream 1310, which acts as a very large cyclewater/glycol bleed.

The overhead vapor withdrawn from the EO stripper 1311 via conduit 1313Ausually contains about 20 to 30 mole % of ethylene oxide. The primarydiluent in this vapor stream is water, although about 7 to 10 mole % canbe generally referred to as non-condensable gases, and is predominantlyCO₂, but also includes nitrogen, argon, oxygen, methane, ethylene andethane. The EO stripper 1311 overhead vapors are cooled in heatexchanger 1312 and the total effluent mixture of uncondensed vapor andcondensate flows via conduits 1313B and 1316 to the EO reabsorber 1327.

The net bleed bottoms stream from the quench section 1352 of column 1300comprises mainly the water formed as a byproduct of the oxidation ofethylene to EO that is partially condensed in the quench scrubbersection 1361/1352 plus makeup wash water from section 1361 and alsocontains some alkaline salts and absorbed ethylene oxide. This stream issent, via conduit 1365, to a small purge stripper 1366 where theabsorbed ethylene oxide is stripped out, using stripping steam injectedvia conduit 1371, or generated in a reboiler (not shown). A purgestripper feed/bottoms heat exchanger may be also used to reduce thereboiler heat duty and/or the amount of stripping steam. The overheadvapors from purge stripper 1366 are cooled in a heat exchanger 1368 to atemperature such that a substantial part, preferably at least 60%, ofthe contained water is condensed. The contaminated condensate phase fromthe condenser 1368 is drained or pumped back into the upper portion ofthe purge stripper 1366 via conduit 1369. The uncondensed overhead vaporfrom purge stripper 1366 is withdrawn from the condenser 1368 viaconduit 1370, combined with the EO and condensate mixture from condenser1312 and the recycled EO vapor in conduit plus the contents of conduit1381A and introduced into a lower portion of the EO Reabsorber 1327 viaconduit 1316. Conduit 1381A contains the combined vented vapors from thefirst lights stripper 1380 (which produces feed to the high purityethylene oxide (HPEO) column 1345), the second lights stripper 1390(which produces the feed to the monoethylene glycol plant 1335) and theHPEO column 1345 in conduit 1316 and introduced into a lower portion ofthe EO reabsorber 1327. The EO-free aqueous bottoms from the purgestripper 1366, containing most of the formaldehyde, salts, and a smallamount of ethylene glycol are sent to waste treatment or technical gradeglycol recovery via conduit 1372.

Some recycle cold water is introduced to an upper portion of the EOreabsorber 1327 via conduit 1351B. Within the upper portion of the EOreabsorber 1327, the light gases in the overhead vapor from EO stripper1311 and the water from conduit 1351B are counter-currently contacted inorder to absorb the maximum amount possible of the ethylene oxidecontained in the vapor into the water. The non-condensable gasesemerging from the top of the EO reabsorber 1327, normally containingonly trace amounts of ethylene oxide are vented via conduit 1328. Sincethis vent stream in conduit 1328 contains a significant amount ofhydrocarbons, comprising mainly ethylene and methane, it is preferablycompressed and recycled back to the EO reactor gas system for maximumrecovery of the contained ethylene. In some plants, particularly thoseof small production capacity, the reabsorber vent gas may be vented toatmosphere, or may be incinerated to avoid atmospheric pollution.

The EO-rich reabsorbate is withdrawn from the bottom of the EOreabsorber 1327 via conduit 1330. This reabsorbate in conduit 1330 ispressurized using a pump (not depicted) and divided into three portions.The first portion of reabsorbate from EO reabsorber 1327 is recycled viaconduit 1332, mixed with EO bypass from conduit 1326 in conduit 1333A,cooled in heat exchanger 1329 and fed to the middle of the EO reabsorbercolumn 1327.

The second portion of reabsorbate from EO reabsorber 1327 is the largestportion of the net bottoms product and flows through conduits 1331 and1379 to the top of the first lights stripper 1380 (also referred to asthe HPEO lights stripper 1380).

The third portion of reabsorbate from the EO reabsorber 1327 is thebalance of the net bottoms product and flows through conduits 1331,1387, 1388 and 1389 to the top of the second lights stripper 1390, alsoreferred to as the MEG lights stripper 1390. Notably, the aqueousreabsorbate from EO reabsorber 1327 contains not only the reabsorbedethylene oxide vapor from the EO stripper 1311, but also containsdissolved carbon dioxide and non-condensable gases that need to beremoved before the stream can be fed to the glycol reactor, 1335.Degasifying the third portion of reabsorbate and the gasified diluentbypassed absorbate is the purpose of this second lights stripper 1390.

The flow rate of the EO-rich reabsorbate from the EO reabsorber 1327 tothe HPEO (first) lights stripper 1380 is controlled to supply only theexact quantity of EO feed required by the HPEO Column 1345. In the firstlights stripper 1380, the reabsorbate feed to the HPEO column 1345 isstripped of carbon dioxide and other light gases using stripping steamthat is supplied to the bottom of the column 1345 from the evaporationtrain 1337 via conduits 1338 and 1338A. The gas-free bottoms from thefirst lights stripping column 1380 are then pumped and fed to the lowerpart of EO purification column 1345 via conduits 1344A and 1344B andpreheater 1343.

In the high purity EO (HPEO) purification column 1345, the reabsorbatefeed (conduit 1344B) is separated into a purified side-stream EO liquidproduct (stream 1346), a small formaldehyde-rich crude EO overhead vaporpurge stream (stream 1347) that is recycled back to the EO reabsorber1327 for recovery of the EO, and an impure side stream ofacetaldehyde-rich EO that is removed via conduit 1341 and sent to theMEG (second) lights stripper 1390 to be fed to the glycol reaction unit1335. An EO-free bottoms water stream containing most of the traceamount of formaldehyde in the purification column 1345 feed, iswithdrawn from column 1345 via conduit 1349A, cooled in heat exchanger1343 and a portion is recycled to the EO reabsorber 1327 via conduits1349B, 1351A, and 1351B. The EO-free bottoms not required in thereabsorber 1327 is recycled via conduit 1342, to be combined withrecycle condensate from the evaporation train 1337 in conduit 1339B.

The balance of the total EO-rich reabsorbate withdrawn from EOreabsorber 1327 via conduit 1331 that is not fed to HPEO (first) lightsstripper 1380 is withdrawn via conduit 1387, mixed with the part of thetotal bypass absorbate that is withdrawn via conduit 1386 and aftercombining with the acetaldehyde-EO purge stream in conduit 1341 from ahigh purity EO column 1345, the entire mixture is fed to the top of MEG(second) lights stripper 1390 via conduit 1389. The concentration of theEO in the 1386 conduit is sufficiently low to dilute the feed mixture inconduit 1389 such that the bottoms product from the second lightsstripper 1390 in conduit 1334 is the appropriate low EO concentration tobe fed to the glycol reactor 1335. Importantly, the EO/water in the 1386conduit has bypassed both the EO stripper 1311 and the EO reabsorber1327.

Optionally, the lights-free acetaldehyde-EO purge stream in conduit 1341(from high purity EO column 1345) can be injected into the bottom of thesecond lights stripper 1390 to minimize the amount of acetaldehyde thatis contained in the overhead vapor from the second lights stripper 1390.

Stripping steam is supplied from the evaporation train 1337 via conduits1338 and 1338C to the bottom of the MEG (second) lights stripper 1390.The light gases that are stripped out exit the second lights stripper1390 via conduit 1391 and are combined with formaldehyde-rich gas fromthe EO purification column 1345 in conduits 1391A, CO₂ rich product fromthe HPEO (first) lights stripper 1380 in conduit 1381A and then combinedwith vapor/liquid effluent from the cooler 1312 and the top vaporproduct of the small purge stripper 1366 in conduit 1316, entering thebottom of the EO reabsorber 1327. The gas-free bottoms productcontaining EO and water from the MEG (second) lights stripper 1390 isthen pumped to the glycol reaction unit 1335 via conduit 1334, as notedabove.

In the glycol reactor 1335, the ethylene oxide in the degasified secondlights stripper 1390 bottoms is almost completely reacted with water toform ethylene glycols. The effluent from the glycol reactor 1335 is fedto the multiple-effect evaporation train 1337 in which the water isseparated from the concentrated crude glycol that is then fed to aglycol purification process (not shown) via conduit 1340. Part of thewater separated in the evaporation train 1337 is recycled back to thevarious unit operations (as described above) of the EO plant as steamvia conduits 1338 and injected directly into the HPEO (first) lightsstripper 1380 (via conduit 1338A), MEG (second) lights stripper 1390(via conduit 1338C) and the EO stripper 1311 (via conduit 1338B) toprovide up to 100% of the required stripping steam. Steam from theevaporation train 1337 may also be utilized for the high purity ethyleneoxide distillation column 1345.

The balance of the recovered evaporation condensate from the glycolevaporation train 1337 is recycled back to the EO plant via conduit 1339and combined with the balance of the bottoms from the EO purificationcolumn 1345 in conduit 1339B. To provide the required flow of absorptionwater to the EO absorber section 1303, makeup recycle water is added viaconduits 1339B, 1339C, 1321A and 1321B and surplus recycle water is sentto a recycle surge tank (not shown) via conduit 1339D.

FIG. 4 is a graph showing the effect of increasing the water:EO ratio onthe glycol reactor product distribution, demonstrating the necessity ofhaving a more dilute ethylene oxide and water concentration to feed theglycol reactor 335 or 1335.

Non-limiting Aspects of the invention are as follows:

Aspect 1: A process for producing purified ethylene oxide (EO) andmonoethylene glycol (MEG), the process comprising the steps of:

a) providing a quenched and alkaline treated and water washed vaporousreaction stream, wherein the quenched and alkaline treated and waterwashed vaporous reaction stream comprises EO, CO₂, formaldehyde, andacetaldehyde;

b) contacting the quenched and alkaline treated and water washedvaporous reaction stream with water in an EO absorber to produce a firstabsorbate stream having a first EO concentration in water;

c) dividing the first absorbate stream into a first portion of the firstabsorbate stream, a second portion of the first absorbate stream, and athird portion of the first absorbate stream;

d) feeding the first portion of the first absorbate stream to an EOstripper and contacting the first portion of the first absorbate streamwith steam to produce a vaporous EO stream;

e) feeding the vaporous EO stream to an EO reabsorber and contacting thevaporous EO stream with the second portion of the first absorbate streamto form a reabsorber bottoms stream, wherein the reabsorber bottomsstream has a second EO concentration in water that is higher than thefirst EO concentration in water;

f) dividing the reabsorber bottoms stream into a first portion of thereabsorber bottoms stream and a second portion of the reabsorber bottomsstream;

g) feeding the first portion of the reabsorber bottoms stream to a firstlights stripper and contacting the first portion of the reabsorberbottoms stream with steam to produce a first lights stripper bottoms,wherein the first light stripper bottoms has a third EO concentration inwater that is higher than the first EO concentration in water;

h) feeding the first lights stripper bottoms to a high purity ethyleneoxide distillation column to produce purified EO;

i) combining the second portion of the reabsorber bottoms stream and thethird portion of the first absorbate stream to produce a second lightsstripper feed;

j) feeding the second lights stripper feed to a second lights stripperand contacting the second lights stripper feed with steam to produce asecond lights stripper bottom stream, wherein the second lights bottomstream has a fourth EO concentration in water that is lower than thethird EO concentration in water; and

k) feeding the second lights bottom stream to a glycol reactor toproduce MEG.

Aspect 2: The process according to Aspect 1, wherein the first portionof the first absorbate stream is 30 wt. % to 80 wt. % of the firstabsorbate stream, the second portion of the first absorbate stream is 15wt. % to 50 wt. % of the first absorbate stream, and the third portionof the first absorbate stream is 5 wt. % to 40 wt. % of the firstabsorbate stream.

Aspect 3: The process according to any of Aspects 1 and 2, wherein thefirst portion of the first absorbate stream is 40 wt. % to 60 wt. % ofthe first absorbate stream, the second portion of the first absorbatestream is 25 wt. % to 35 wt. % of the first absorbate stream, and thethird portion of the first absorbate stream is 10 wt. % to 25 wt. % ofthe first absorbate stream.

Aspect 4: The process according to any of Aspects 1-3, wherein the highpurity ethylene oxide distillation column further produces a purgestream comprising ethylene oxide and acetaldehyde and wherein the purgestream comprising ethylene oxide and acetaldehyde is fed to the secondlights stripper.

Aspect 5: The process according to any of Aspects 1-4, wherein the highpurity ethylene oxide distillation column produces a vaporous overheadstream comprising EO and formaldehyde and the vaporous overhead streamcomprising EO and formaldehyde is fed to the EO reabsorber with thevaporous EO stream.

Aspect 6: The process according to any of Aspects 1-5, wherein the firstlights stripper produces a vaporous overhead stream that comprises CO₂and the vaporous overhead stream that comprises CO₂ is fed to the EOreabsorber with the vaporous EO stream.

Aspect 7: The process according to any of Aspects 1-6, wherein anevaporation train after the glycol reactor provides steam to at leastone of the EO stripper, the first lights stripper, the second lightsstripper, and the high purity ethylene oxide distillation column.

Aspect 8: The process according to any of Aspects 1-7, wherein the waterthat is contacted with the quenched and alkaline treated and waterwashed vaporous reaction stream in the EO absorber comprises recycledprocess water.

Aspect 9: The process according to any of Aspects 1-8, wherein the highpurity ethylene oxide distillation column further produces a purgestream comprising the acetaldehyde and EO, and wherein step i) furthercomprises combining the purge stream comprising the acetaldehyde and EOwith the second lights stripper feed.

Aspect 10: An apparatus for producing purified ethylene oxide (EO) andmonoethylene glycol (MEG) from a quenched and alkaline treated and waterwashed vaporous reaction stream, wherein the quenched and alkalinetreated and water washed vaporous reaction stream comprises EO, CO₂,formaldehyde, and acetaldehyde, the apparatus comprising:

a) an EO absorber configured and arranged to contact the quenched andalkaline treated and water washed vaporous reaction stream with water toproduce a first absorbate stream having a first EO concentration inwater;

b) a first series of conduits configured and arranged to divide thefirst absorbate stream into a first portion of the first absorbatestream, a second portion of the first absorbate stream, and a thirdportion of the first absorbate stream;

c) an EO stripper configured and arranged to contact the first portionof the first absorbate stream with steam to produce a vaporous EOstream;

d) an EO reabsorber configured and arranged to contact the vaporous EOstream with the second portion of the first absorbate stream to form areabsorber bottoms stream, wherein the reabsorber bottoms stream has asecond EO concentration in water that is higher than the first EOconcentration in water;

e) a second series of conduits configured and arranged to divide thereabsorber bottoms stream into a first portion of the reabsorber bottomsstream and a second portion of the reabsorber bottoms stream;

f) a first lights stripper configured and arranged to contact the firstportion of the reabsorber bottoms stream with steam to produce a firstlights stripper bottoms, wherein the first light stripper bottoms has athird EO concentration in water that is higher than the first EOconcentration in water;

g) a high purity ethylene oxide distillation column configured andarranged to produce purified EO from the first lights stripper bottoms;

h) a series of conduits configured and arranged to combine the secondportion of the reabsorber bottoms stream and the third portion of thefirst absorbate stream to produce a second lights stripper feed;

i) a second lights stripper configured and arranged to contact thesecond lights stripper feed with steam to produce a second lightsstripper bottom stream, wherein the second lights bottom stream has afourth EO concentration in water that is lower than the third EOconcentration in water; and

j) a glycol reactor configured and arranged to produce MEG from thesecond lights bottom stream.

Aspect 11: The apparatus according to Aspect 10, further comprising anevaporation train after the glycol reactor, wherein the evaporationtrain is configured and arranged to provide steam to at least one of theEO stripper, the first lights stripper, the second lights stripper, andthe high purity ethylene oxide distillation column.

Aspect 12: The apparatus according to any of Aspects 10 and 11, whereinthe high purity ethylene oxide distillation column is further configuredand arranged to produce a purge stream comprising the acetaldehyde andEO, and wherein h) is further configured and arranged to combine thepurge stream comprising the acetaldehyde and EO with the second lightsstripper feed.

Example: (Prophetic)

An EO plant has an EO reactor with a capacity to produce 260,000 metrictons per year (T/yr.) of EO, equivalent to 31.25 metric tons per hour(T/hr.) as feed to both a monoethylene glycol (MEG) plant that canprocess 100% of the EO and to an EO purification system with a capacityof 150,000 metric tons per year (T/yr.) of high purity ethylene oxide(HPEO). The EO purification section includes an EO stripper bypassstream (as shown in FIG. 2 ) and the EO stripper/reabsorber system isdesigned to produce 10 wt. EO in water feed to the high purity ethyleneoxide (HPEO) column and to the MEG reactor, which permits 25% of the EOabsorbate to bypass the EO stripper and reduces the stripping steam flowto the EO Stripper by 25% or about 11 tons per hour (T/hr.).

During normal operation with 10 wt. % EO in water, the EO feed to theMEG reactor is only 42% of the design capacity of the MEG reactor system(the combination of the MEG reactor and the evaporation train after thereactor). Therefore the amount of process steam that can be provided tothe EO recovery and purification sections from the evaporation train ofthe MEG reactor system is much lower than the amount of steam requiredby the EO recovery section alone. Accordingly, the optimum EOconcentration in the feed to the MEG reactor will normally be much lowerthan 10 wt. % in water so as to increase the amount of stripping steamthat can be extracted from the evaporation train of the MEG reactorsystem and to reduce the undesirable formation of diethylene glycol(DEG) and triethylene glycol (TEG) and raise the yield of the desiredMEG. As shown in FIG. 2 , the water that would be normally be used todilute the EO feed to the MEG reactor would be recycled EO-free processwater (mainly process condensate from the evaporator section of theglycol reactor system) and as a result, the final EO concentration ofthe MEG reactor feed cannot affect the amount of absorbate that bypassesthe EO Stripper.

As shown in FIG. 3 , by installing a second lights stripper that wouldbe used to degasify only the final diluted EO feed to the MEG reactor,all the diluent water required for the MEG reactor feed can be providedfrom additional absorbate that will bypass both the EO stripper and theEO reabsorber. Detailed simulations of the EO plant show that bydiluting the EO feed to the MEG reactor to the maximum waterconcentration that the evaporation section can handle, the EOconcentration would be about 6.4 wt. % (equivalent to a water to{EO+MEG} molar ratio of 33:1). To provide the required diluent water, anadditional 14% of the EO absorbate would bypass the EO stripper and theEO reabsorber, resulting in a total of 40% of the absorbate bypassingthe EO stripper. This additional bypass provides a total reduction instripping steam usage of 17 T/hr. (i.e., an additional 6 T/hr. of steamcan be saved due to the enhanced EO bypass).

In both the standard and enhanced EO bypass cases, the justification forincreasing the water to {EO+MEG} molar ratio from about 22:1 (with 10wt. % EO) to about 33:1 would be an increase in the MEG yield to about92.5 wt. % (from about 90 wt. %) as shown in FIG. 4 . The higher waterconcentration would result in an increase in the high pressure andmedium pressure steam usage in the MEG reaction preheat and evaporationtrains that largely would be offset by the increased low pressureprocess steam that would be extracted from the evaporation train andused in the EO plant in both cases.

What is claimed:
 1. An apparatus for producing purified ethylene oxide(EO) and monoethylene glycol (MEG) from a quenched and alkaline treatedand water washed vaporous reaction stream, wherein the quenched andalkaline treated and water washed vaporous reaction stream comprises EO,CO₂, formaldehyde, and acetaldehyde, the apparatus comprising: a) an EOabsorber configured and arranged to contact the quenched and alkalinetreated and water washed vaporous reaction stream with water to producea first absorbate stream having a first EO concentration in water; b) afirst series of conduits configured and arranged to divide the firstabsorbate stream into a first portion of the first absorbate stream, asecond portion of the first absorbate stream, and a third portion of thefirst absorbate stream; c) an EO stripper configured and arranged tocontact the first portion of the first absorbate stream with steam toproduce a vaporous EO stream; d) an EO reabsorber configured andarranged to contact the vaporous EO stream with the second portion ofthe first absorbate stream to form a reabsorber bottoms stream, whereinthe reabsorber bottoms stream has a second EO concentration in waterthat is higher than the first EO concentration in water; e) a secondseries of conduits configured and arranged to divide the reabsorberbottoms stream into a first portion of the reabsorber bottoms stream anda second portion of the reabsorber bottoms stream; f) a first lightsstripper configured and arranged to contact the first portion of thereabsorber bottoms stream with steam to produce a first lights stripperbottoms, wherein the first lights stripper bottoms has a third EOconcentration in water that is higher than the first EO concentration inwater; g) a high purity ethylene oxide distillation column configuredand arranged to produce purified EO from the first lights stripperbottoms; h) a series of conduits configured and arranged to combine thesecond portion of the reabsorber bottoms stream and the third portion ofthe first absorbate stream to produce a second lights stripper feed; i)a second lights stripper configured and arranged to contact the secondlights stripper feed with steam to produce a second lights stripperbottom stream, wherein the second lights stripper bottom stream has afourth EO concentration in water that is lower than the third EOconcentration in water; and j) a glycol reactor configured and arrangedto produce MEG from the second lights stripper bottom stream.
 2. Theapparatus according to claim 1, further comprising an evaporation trainafter the j) glycol reactor, wherein the evaporation train is configuredand arranged to provide steam to at least one of the c) EO stripper, thef) first lights stripper, the i) second lights stripper, or the g) highpurity ethylene oxide distillation column.
 3. The apparatus according toclaim 1, further comprising an evaporation train after the j) glycolreactor, wherein the evaporation train is configured and arranged toprovide steam to the c) EO stripper.
 4. The apparatus according to claim1, further comprising an evaporation train after the j) glycol reactor,wherein the evaporation train is configured and arranged to providesteam to the f) first lights stripper.
 5. The apparatus according toclaim 1, further comprising an evaporation train after the j) glycolreactor, wherein the evaporation train is configured and arranged toprovide steam to the i) second lights stripper.
 6. The apparatusaccording to claim 1, further comprising an evaporation train after thej) glycol reactor, wherein the evaporation train is configured andarranged to provide steam to the g) high purity ethylene oxidedistillation column.
 7. The apparatus according to claim 1, wherein theg) high purity ethylene oxide distillation column is further configuredand arranged to produce a purge stream comprising the acetaldehyde andEO, and wherein the h) series of conduits is further configured andarranged to combine the purge stream comprising the acetaldehyde and EOwith the second lights stripper feed.
 8. The apparatus according toclaim 1, wherein the g) high purity ethylene oxide distillation columnis configured and arranged to produce a vaporous overhead streamcomprising EO and formaldehyde and wherein the g) high purity ethyleneoxide distillation column is configured and arranged to feed thevaporous overhead stream comprising EO and formaldehyde to the d) EOreabsorber.
 9. The apparatus according to claim 1, wherein the f) firstlights stripper is configured and arranged to produce a vaporousoverhead stream that comprises CO₂ and wherein the f) first lightsstripper is configured and arranged to feed the vaporous overhead streamthat comprises CO₂ to the d) EO reabsorber.